🌀 Friction – MCQs for Class 8 Science

Part 3: Q51–Q75

Q51. When brakes are applied in a moving bicycle, which friction acts between brake pads and wheel?

A) Rolling friction
B) Sliding friction
C) Static friction
D) Fluid friction

✅ Correct Answer: B) Sliding friction

Explanation:

• A) Wheels roll on ground, not here.
• B) ✔ Brake pads rub → sliding friction slows motion.
• C) Acts when at rest.
• D) Not relevant.

Q52. The friction that helps tyres grip the road is:

A) Rolling friction
B) Static friction
C) Sliding friction
D) Fluid friction

✅ Correct Answer: B) Static friction

Explanation:

• A) Wheels roll, but grip is due to static friction.
• B) ✔ Provides grip → prevents slipping.
• C, D – Not main reason.

Q53. Which of these factors does NOT affect friction?

A) Roughness of surface
B) Nature of surface
C) Mass of object
D) Colour of surface

✅ Correct Answer: D) Colour of surface

Explanation:

• D) ✔ Colour does not affect friction.

Q54. On which surface is friction maximum?

A) Smooth glass
B) Polished marble
C) Rough concrete
D) Ice

✅ Correct Answer: C) Rough concrete

Explanation:

• C) ✔ More irregularities → maximum friction.

Q55. When a block is dragged over a rough surface, work is done against:

A) Gravity
B) Friction
C) Normal force
D) Thrust

✅ Correct Answer: B) Friction

Explanation:

• B) ✔ Energy is spent overcoming resistive force.

Q56. Why does a ball stop rolling on ground after some distance?

A) Air drag only
B) Gravitational pull only
C) Friction with ground and air
D) Lack of force applied

✅ Correct Answer: C) Friction with ground and air

Explanation:

• C) ✔ Friction and air resistance oppose motion.

Q57. Which type of friction is useful for writing on a blackboard with chalk?

A) Static friction
B) Rolling friction
C) Sliding friction
D) Fluid friction

✅ Correct Answer: C) Sliding friction

Explanation:

• C) ✔ Chalk rubs on board, leaving marks.

Q58. Which type of friction is responsible when a heavy box is just about to move?

A) Rolling friction
B) Limiting friction
C) Sliding friction
D) Fluid friction

✅ Correct Answer: B) Limiting friction

Explanation:

• B) ✔ Maximum static friction before sliding begins.

Q59. Which of the following has the least resistance to motion?

A) Static friction
B) Sliding friction
C) Rolling friction
D) Limiting friction

✅ Correct Answer: C) Rolling friction

Explanation:

• C) ✔ Rolling friction is least.

Q60. If friction were absent, we could not:

A) Walk
B) Write
C) Drive vehicles
D) All of these

✅ Correct Answer: D) All of these

Explanation:

• D) ✔ All daily activities depend on friction.

Q61. Friction can be increased by:

A) Lubricating
B) Making surface rough
C) Using ball bearings
D) Polishing

✅ Correct Answer: B) Making surface rough

Explanation:

• B) ✔ Roughness increases grip.

Q62. In which case do we want to reduce friction?

A) Walking
B) Brakes of vehicles
C) Machine parts
D) Climbing stairs

✅ Correct Answer: C) Machine parts

Explanation:

• C) ✔ Reduced friction saves energy and wear.

Q63. Which factor increases rolling friction?

A) Smooth surface
B) Rough surface
C) Lubrication
D) Ball bearings

✅ Correct Answer: B) Rough surface

Explanation:

• B) ✔ Roughness increases resistance even in rolling motion.

Q64. Which one of these is an advantage of friction?

A) Produces noise
B) Produces heat in machines
C) Provides grip for walking
D) Causes energy loss

✅ Correct Answer: C) Provides grip for walking

Explanation:

• C) ✔ Without friction, walking is impossible.

Q65. Which of these shows that friction produces heat?

A) Hands warm on rubbing
B) Tyres get hot after driving
C) Machine parts heat up
D) All of these

✅ Correct Answer: D) All of these

Explanation:

• D) ✔ Heat is generated in all examples due to rubbing.

Q66. Sliding friction between two surfaces depends on:

A) Normal force and nature of surfaces
B) Shape of object only
C) Colour of surfaces
D) Time of contact

✅ Correct Answer: A) Normal force and nature of surfaces

Explanation:

• A) ✔ Heavier objects and rough surfaces → more friction.

Q67. Why do athletes wear studded shoes?

A) To reduce speed
B) To look stylish
C) To increase friction
D) To reduce friction

✅ Correct Answer: C) To increase friction

Explanation:

• C) ✔ Studs grip ground → prevent slipping.

Q68. What is drag?

A) Friction in solids
B) Friction in liquids
C) Friction in gases
D) Friction in fluids

✅ Correct Answer: D) Friction in fluids

Explanation:

• D) ✔ Drag = resistance in both liquids and gases.

Q69. Which device uses the principle of reducing friction by rolling?

A) Barometer
B) Ball bearing
C) Thermometer
D) Magnet

✅ Correct Answer: B) Ball bearing

Explanation:

• B) ✔ Converts sliding into rolling friction.

Q70. What happens to friction when surfaces are polished?

A) Increases
B) Decreases
C) Remains same
D) Becomes infinite

✅ Correct Answer: B) Decreases

Explanation:

• B) ✔ Smooth polished surfaces reduce irregularities → less friction.

Q71. Which of the following is a fluid friction example?

A) Car tyres on road
B) Boat moving in water
C) Box sliding on floor
D) Chalk on blackboard

✅ Correct Answer: B) Boat moving in water

Explanation:

• B) ✔ Water opposes motion = fluid friction.

Q72. Why is oil applied on cycle chains?

A) To make them shine
B) To reduce friction
C) To increase weight
D) To increase grip

✅ Correct Answer: B) To reduce friction

Explanation:

• B) ✔ Oil lubricates chain links → smoother motion.

Q73. Which friction helps in driving cars on road?

A) Rolling
B) Static
C) Sliding
D) Fluid

✅ Correct Answer: B) Static

Explanation:

• B) ✔ Static friction gives grip → prevents tyres from slipping.

Q74. What is the main disadvantage of friction?

A) It prevents slipping
B) It reduces efficiency of machines
C) It allows writing
D) It helps walking

✅ Correct Answer: B) It reduces efficiency of machines

Explanation:

• B) ✔ Energy wasted as heat → lower efficiency.

Q75. When a person rubs hands together in winter, they feel warm because:

A) Blood circulation increases
B) Friction produces heat
C) Muscles generate heat
D) Sunlight reflection

✅ Correct Answer: B) Friction produces heat

Explanation:

• B) ✔ Rubbing → friction → warmth.

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